Glycosylation is a post translational modification that is crucial in various stages of development, differentiation and oncogenesis (1-7). Glycan modification is a dynamic process involved in cell-signaling and cell-interaction. Glycans are receptors for a variety of ligands such as toxins, antibodies, bacteria, viruses, cellular receptors and lectins (8-18).
The first glycan biomarker for drug response and multidrug resistance was disclosed in U.S. Pat. No. 7,585,503, issued Sep. 8, 2009, which is incorporated herein by reference in its entirety (19). In brief, U.S. Pat. No. 7,585,503 describes flow cytometry to evaluate the distribution of cell surface sialic acids on isogenic cell line pairs, each pair comprising a drug-sensitive parental isotype and its drug-resistant off-spring phenotype. Comparison of the sialic acid profiles of each set of drug-susceptible and drug-resistant isogenic pairs revealed a distinct decrease in the amounts of alpha 2-6 sialic acid motif (hereinafter “AD6”) on the surface of drug-resistant cells compared to their drug-sensitive isotypes in all of the isogenic cell pairs.